If winter driving makes you short on traction, tires can be loaded with fluid or wrapped with chains to beef up their bite.ISTOCKPHOTO.COM/LORI SPARKIA

Finding a tractor to fit the task is imperative, as the owners of this Sonoma County, California, vineyard discovered.ISTOCKPHOTO.COM/GALINA BARSKAYA

Never operate a tractor on a public road without an approved Slow Moving Vehicle (SMV) emblem.ISTOCKPHOTO.COM/PHIL BERRY

Caution sign for moving tractors.ISTOCKPHOTO.COM/MICHELLE JUNIOR

How to choose a tractor that is right for your farm.

When Charles W. Hart and Charles H. Parr first coined the term tractor in reference to one of their petroleum-powered pieces about a century ago, they described a machine capable of easing the physical burden on farms of all sizes. Although the steel-wheeled contraptions that Hart-Parr Manufacturing Co. first offered bear little resemblance to today's sleek, smooth-running machines, their early success was sufficient to provide the foundation for one of the longest-running and most recognizable symbols of modern agriculture.

In the early years, tractors had engines, drive trains (complete with clutches, transmissions and rear axles), stationary power drive systems (belt-pulleys and power take-offs PTOs), and a drawbar for pulling. Step forward a few years to the arrival of specialized hitches for mounted implements and hydraulic systems to raise and lower them, offering even more versatility. Today's tractors are as fully evolved as our computer-controlled cars and trucks. On the surface, they still have most of their predecessors' principal components. But those components have changed dramatically, and in many cases include two or more variations.

When shopping for a new (or recent-used) tractor, buyers choose more than just engine size and hitch equipment. There are no fewer than four discrete types of transmissions, at least three styles of tires and two drive systems to decide on, in addition to drawbars, hydraulic outlets, operator amenities, ballast and more. Making informed choices when putting together a new tractor or carefully choosing a used model is key to having a fully functional, enjoyable and safe farm power experience.

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How to Choose a Tractor: Horsepower with Bite

Tractor marketing pitches universally point to engine power to lure prospective buyers, but that isn't the most useful number when trying to understand a machine's capabilities. No one would ask a 25-horsepower lawn tractor weighing 750 pounds to do the same kind of work expected from a 4,000-pound, 25-horsepower farm tractor. A better measure of a tractor's capabilities comes from drawbar and PTO ratings, which will be much higher for the farm tractor than the lawn tractor.
Although the value is different for each machine, most tractors offer between 75 and 85 percent of their engine's power at the PTO, which is then available to run powered implements such as balers or mowers. The tractor's drawbar horsepower, on the other hand, cannot be accurately estimated from engine power because it depends on the tractor's weight, tires and traction characteristics. In the same operating conditions, the heavier of two otherwise identical tractors will have more pulling power, but tire patterns will also make a difference.

For most tractors, drive wheels equipped with bar-lug agricultural (R-1) tires will offer the best traction in the field, although industrial (R-4) tires also work well and make a good choice for tractors that spend significant time under a loader or on the road. Turf-type (R-3) tires have the least aggressive lugs and offer the least traction overall, but they don't mangle nicely manicured lawns. In any case, if you are short on traction, the tires can be loaded with fluid for added weight, wrapped with chains — or both — to beef up their bite.

Dealing with Diesels

Most new tractors today are powered with fuel-efficient, diesel engines that meet or exceed current emission standards. These modern mills are easy to start and simple to maintain, and they have life expectancies of many thousands of hours.

Operating a diesel engine is not terribly different from the more familiar gasoline engine, but you need to be aware of seasonal fuel variations, cold weather starting procedures and other diesel system quirks to get the most from your tractor.

Unlike gasoline-fueled engines, diesels rely on cylinder pressure to ignite a precise injection of atomized fuel. Due to the high cylinder pressures, cranking a diesel to life requires a high-amperage battery and powerful electric starter, but in some weather that's still not enough. Cold diesel engines can't always generate the heat required for ignition, so they are equipped with battery-powered starting aids such as glow plugs or intake air heaters. Once they are sufficiently warmed, they run on their own.

Diesel fuel is made with hydrocarbon molecules that are on average much longer than those found in gasoline. As a consequence, diesel packs more calories into a gallon than gasoline, but diesel also has a higher melting point, which can cause gelling in single-digit temperatures (depending on the precise formulation). Gelled fuel clogs delivery lines and filters and prevents a diesel engine from running. In cold climates, suppliers offer winterized diesel blends that stay liquid to temperatures below minus-20 degrees. As long as the glow plugs, batteries and fuel system are in good shape and there is a winter blend in the tank, engine starts in cold climates need not be a problem.

Diesel is also a favored food of some fungi and bacteria, and they can set up housekeeping, causing problems with fuel-system clogging and acidification, which leads to serious corrosion in aluminum tanks. Operators who regularly change the fuel system's filters and who use fresh diesel rarely have a problem, although many also use additives to keep the microbial morass to a minimum.

To Clutch or Not to Clutch

It used to be that power from a tractor's engine was transmitted through a clutch to a simple sliding-gear primary transmission before heading to the drive wheels. Those somewhat cumbersome gearboxes required clutching and stopping the tractor before shifting.

Today, that same type of primary transmission is used in some economy tractor lines, but synchronized (called synchromesh in some references) transmissions, which employ special internal clutches to match gear speeds during a shift, are more likely. When the gears are synchronized, gear changes while the tractor is moving (after depressing the clutch pedal) are easily accomplished without grinding.

Some manufacturers have taken this design one step further and offer so-called clutch-free shifting. For example, with Kubota's Glide Shift Transmission (GST), moving the gear lever from its locked position automatically disengages the clutch, using hydraulics. With the shift completed, the clutch automatically reengages. This system is useful for shifting on the fly with rolling loads, but with ground-engaging loads, gear changes require a powershift transmission, which is typically found only in larger, more powerful farm tractors. Small tractor owners do have an option when speed changes under load are required.

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The hydrostatic primary transmission (standard equipment on John Deere's model 2520 compact) offers continuously variable speed changes while the tractor is under any rated load. This gearless design features an engine-driven variable-displacement hydraulic pump that supplies high-pressure oil to a hydraulic motor causing it to spin. To make the tractor go faster, the operator simply pushes a pedal (or pulls a lever) to increase the pump's displacement, which causes the hydraulic motor to spin faster without affecting the engine speed. Reducing the pump's displacement to nothing brings the hydraulic motor, and thus the tractor, to an abrupt halt. The most user-friendly hydro control system employs a single pivoting foot pedal. Rock the pedal slightly forward or backward and the tractor creeps in the indicated direction. More rocking and the tractor's speed increases. Return the pedal to the neutral position and the tractor stops.

Range Transmission Roundup

Matching ground speed to optimal engine speed is critical for efficient tractor operation and more transmission speeds are always an advantage. One of the easiest ways to multiply the number of drive gears is to place a range transmission in series with the primary transmission. Range transmissions minimally offer high and low settings, although three or four ranges are not uncommon; some also handle reverse. A tractor like Montana's model 3040 with a four-speed primary and a three-speed range transmission has 12 total forward speeds. If reverse is located in the primary, then four reverse speeds are available; if it is only in the range transmission there will be three reverse speeds. With Montana's 3040, reverse is handled separately, and the tractor has 12 reverse gears, too.

Tractors with hydrostatic primary transmissions also benefit from an added range transmission and several manufacturers offer the combination. For example, Kubota's hydrostatic L-3130 HST is equipped with a three-speed, non-synchronized, sliding gear, range transmission that gives the machine infinite adjustment up to three different top speeds in both forward and reverse. Low range and the hydro are perfect for excavating with a front-end loader while the added speed of high range is good for running on the road.

Loader-Friendly Transmissions

Any tractor equipped with a front-end loader will save its operator hours of backbreaking labor and, in many cases, facilitate chores that couldn't be accomplished any other way. Loader work invariably involves high frequency directional changes and, most of the time, a lower gear is needed in forward than what is needed in reverse. All primary/range transmission combinations will work for operating a loader, but some are much better suited.

The hydrostatic primary transmission is arguably the most loader friendly, especially when direction and speed are controlled with a single foot pedal since that leaves the left hand for steering and the right for loader control. Don't rule out the less expensive gear-driven transmissions though. Many gear transmissions can be ordered with a reversing attachment called a shuttle that allows direction changes independent of primary and range transmission settings.

With a shuttle transmission (like that found on Farmtrac's model 300DTC), an operator need only clutch and move a lever forward or backward to select forward or reverse gears. Some range transmissions also allow convenient straight-line shifting between one range setting and reverse in shuttle-like fashion (a few manufacturers call it a shuttle). Most small farm owners don't use more than a single range with shuttle transmissions anyway so this might be a more economical compromise.

Hitching Up Your Tractor

Although there were several proprietary tractor hitches available into the 1960s, Harry Ferguson's three-point leveling hitch (as modified by Ford) was far and away the most popular and provided the basis for the American Society of Agricultural Engineers (ASAE) standards for tractor hitches. The three-point hitch consists of a pair of lower links (hydraulically controlled with lift arms) and a single top link that attach to the implement with different sized pins, depending on the hitch's classification.

Category 1 three-point hitches are typical for tractors between 20 and 45 horsepower while Category 2 hitches are installed on tractors up to about 95 horsepower. Tractors in the 50 to 60 horsepower range are often found with hybrid hitches that can accept both Category 1 and Category 2 implements. Purchase a tractor with a Category 1 hitch, and any Category 1 implement will fit. However, check your tractor's specification list to ensure that the lift can handle the implement's weight.

Hydraulic Power for Tractors

Most modern tractors are equipped with a continuously running hydraulic system that handles the tractor's power steering, three-point hitch and remote (loader, log splitter, auxiliary cylinder) requirements. The system consists of a pump, oil reservoir (usually the transmission housing), steering valve and cylinder, three-point hitch valve(s) and cylinder(s), and expandability to add one to several auxiliary remote valves to operate other equipment. Hydraulic capacity is measured in gallons per minute and that flow is delivered under considerable pressure. With sufficient capacity, a tractor's hydraulic system can be used to spin remote hydraulic motors in addition to powering cylinders.

Tractor hydraulic systems don't experience demand for their full capacity much of the time, but if you plan to mount a loader on the tractor or any rear implements with heavy hydraulic needs such as a hydraulically powered mower or back hoe, you will want be sure that you have enough capacity to supply the highest-demand implement at the very least. It's not necessary to add their requirements together since you won't use the loader while mowing, or the backhoe while loading. However, you will need to work the three-point hitch's lift while operating the hydraulically powered mower, which might cause one or the other to be slow with insufficient capacity.

Experience Tractor Power Take-Off

To get the most out of your farm tractor, it will need at the very least a live rear power take-off (PTO), which can be used to power mounted or trailing mowers, rotary tillers, wood chippers, hay tedders, balers, auxiliary hydraulic systems, you name it. Thanks again to ASAE engineers, these power points have strict dimension, speed and directional specifications. Most small farm tractors have a 540-rpm rear PTO (6 splines, 13/8-inch diameter), although higher-powered tractors usually have a 1,000-rpm (20 splines 1¾-inch diameter) unit in addition. Some compact tractors also have a 1,000- or 2,000-rpm mid-mounted PTO (dimensions are brand-specific) specifically designed to run large lawn-mowing decks.

Like the PTOs that drive them, implements are designed specifically for safe operation at either 540 or 1,000 rpm (some mid-mount mowers operate at 2,000 rpm) and come equipped with PTO shafts sized and splined to fit the correct PTO. PTO-driven implements also have a maximum PTO horsepower rating, which lets you know how much power they can take without damage. A shredder mower with a 35-horsepower gearbox will be damaged in heavy conditions if it is powered with a 50 PTO horsepower tractor. Running the shredder with a 30 PTO horsepower tractor ensures that it will never be overloaded.

Take a Tractor Test Drive

There is no magic formula based on acreage or any other measure that will point you to a specific tractor. Plan to spend part of a season checking out machines from different manufacturers or at least several models from the same manufacturer to get a feel for the different sizes, power ratings and transmission types. Insist on driving them all and, if equipped with loaders, try those as well. Take stock of your property, noting any narrow passages the tractor needs to navigate, and be sure your choice fits there. Take careful inventory of the implements you intend to employ and spend time with implement capacity specifications for tractor models in contention (and/or talk to knowledgeable friends, sales staff, etc.). If you do your homework, the logical choices will become clear fairly quickly.

Oscar "Hank" Will likes engines, gears, and the smell of diesel smoke. When he's not writing about tractors (or photographing them), he's often up to his elbows in transmission fluid making one of his 30-plus-year-old machines ready for the field.

Hank Will raises hair sheep, heritage cattle and many varieties of open-pollinated corn with his wife, Karen, on their rural Osage County, Kansas farm. His home life is a perfect complement to his professional life as editor in chief at GRIT and Capper's Farmer magazines. Connect with him on Google+.

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